U.S. patent number 9,139,958 [Application Number 14/051,971] was granted by the patent office on 2015-09-22 for process for the production of paper.
This patent grant is currently assigned to AKZO NOBEL N.V.. The grantee listed for this patent is Akzo Nobel N.V.. Invention is credited to Johan Nyander, Fredrik Solhage.
United States Patent |
9,139,958 |
Nyander , et al. |
September 22, 2015 |
Process for the production of paper
Abstract
The present invention relates to a process for producing paper
which comprises: (i) providing an aqueous suspension comprising
cellulosic fibers, (ii) adding to the suspension after the last
point of high shear subsequent a centri-screen: (a) a first anionic
component which is a water-soluble anionic anionic polysaccharide;
(b) a second anionic component which is a water-dispersible or
branched acrylamide-based polymer; and (c) a third anionic
component which is an anionic siliceous material comprising an
anionic silica-based polymer comprising anionic silica-based
particles having a specific surface area within the range of from
100 to 1700 m2/g (iii) dewatering the obtained suspension to form
paper.
Inventors: |
Nyander; Johan (Sollentuna,
SE), Solhage; Fredrik (Boras, SE) |
Applicant: |
Name |
City |
State |
Country |
Type |
Akzo Nobel N.V. |
Arnhem |
N/A |
NL |
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Assignee: |
AKZO NOBEL N.V. (Arnhem,
NL)
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Family
ID: |
37417842 |
Appl.
No.: |
14/051,971 |
Filed: |
October 11, 2013 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20140174683 A1 |
Jun 26, 2014 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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13397293 |
Feb 15, 2012 |
8613832 |
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11430341 |
May 9, 2006 |
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60681487 |
May 16, 2005 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
D21H
21/10 (20130101); D21H 17/25 (20130101); D21H
17/37 (20130101); D21H 17/42 (20130101); D21H
17/68 (20130101); D21H 21/52 (20130101); D21H
17/375 (20130101) |
Current International
Class: |
D21H
17/25 (20060101); D21H 17/32 (20060101); D21H
17/37 (20060101); D21H 17/43 (20060101); D21H
23/18 (20060101); D21H 21/10 (20060101); D21H
17/68 (20060101); D21H 17/42 (20060101); D21H
21/52 (20060101) |
Field of
Search: |
;162/158,168.1-168.3,174,175,177,181.1,181.6-181.7,183,185
;524/492,493,500 |
References Cited
[Referenced By]
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WO |
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WO |
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WO |
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Feb 2004 |
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WO |
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Feb 2004 |
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WO |
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Apr 2004 |
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WO |
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Dec 2004 |
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WO |
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WO 2005/116336 |
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Dec 2005 |
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WO |
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Primary Examiner: Cordray; Dennis
Attorney, Agent or Firm: Su; Alice C.
Parent Case Text
This application is a continuation of U.S. application Ser. No.
13/397,293 filed Feb. 15, 2012, which is a divisional of U.S.
application Ser. No. 11/430,341, filed May 9, 2006 (now abandon),
which claims priority based on U.S. Provisional Patent Application
No. 60/681,487, filed May 16, 2005.
Claims
The invention claimed is:
1. A process for producing paper which comprises: (i) providing an
aqueous suspension comprising cellulosic fibres, (ii) adding to the
suspension after the last point of high shear and subsequent a
centri-screen: (a) a first anionic component which is a
water-soluble anionic polysaccharide; (b) a second anionic
component which is a water-dispersible or branched acrylamide-based
polymer; (c) a third anionic component which is an anionic
siliceous material comprising an anionic silica-based polymer
comprising anionic silica-based particles having a specific surface
area within the range of from 100 to 1700 m2/g; (iii) dewatering
the obtained suspension to form paper; wherein the anionic
polysaccharide is selected from the group consisting of cellulose
derivatives.
2. The process of claim 1, wherein the first anionic component has
a weight average molecular weight of at least 10,000.
3. The process of claim 1, wherein the anionic silica-based
particles are present in a sol having an S-value in the range of
from 8 to 50%.
4. The process of claim 1, wherein the anionic silica-based
particles have an average particle size in the range of from 1 to
10 nm.
5. The process of claim 1, wherein the anionic silica-based
particles have a specific surface area in the range of from 50 to
1000 m.sup.2/g.
6. The process claim 1, wherein the anionic silica-based particles
have a specific surface area in the range of from 1000 to 1700
m.sup.2/g.
7. The process of claim 1, wherein the second anionic component has
an unswollen particle size less than 1500 nm.
8. The process of claim 1, wherein the second component has an
unswollen particle size less than 1000 nm.
9. The process of claim 1, wherein the second anionic component is
a water-dispersible or branched acrylamide-based polymer obtained
by polymerization of a monomer mixture comprising polyfunctional
crosslinking agents and monomers selected form the group consisting
of anionic monomers selected from the group consisting of
ethylenically unsaturated carboxylic acids and salts thereof,
ethylenically unsaturated sulphonic acids and salts thereof, and
mixtures thereof; and non-ionic monomers selected from the group
consisting of acrylamide, methacrylamide, N-methyl(meth)acrylamide,
N-ethyl(meth)acrylamide, N-n-propyl(meth)acrylamide,
N-isopropyl(meth)acrylamide, N-n-butyl(meth)acrylamide,
N-t-butyl(meth)acrylamide, N-isobutyl(meth)acrylamide,
N-n-butoxymethyl(meth)acrylamide,
N-isobutoxymethyl(meth)acrylamide, N,N-dimethyl (meth)acrylamide,
N,N-dimethyl(meth)acrylamide, dialkylaminoalkyl (meth) acrylamides,
and mixtures thereof.
10. The process of claim 1, wherein the second anionic component is
a water-dispersible or branched acrylamide-based polymer obtained
by polymerization of a monomer mixture comprising polyfunctional
crosslinking agents and monomers selected form the group consisting
of non-ionic monomers selected from the group consisting of
acrylamide, methacrylamide, and mixtures thereof; and anionic
monomers selected from the group consisting of ethylenically
unsaturated carboxylic acids and salts thereof.
11. The process of claim 1, wherein the first, second and third
anionic components are present in a weight ratio of
0.1-2:0.1-2:1.
12. The process of claim 1, wherein the cellulosic suspension after
addition of the first, second and third anionic components is fed
into a headbox of a paper machine, the headbox ejecting the
suspension onto a forming wire for drainage.
13. A process for producing paper which comprises: (i) providing an
aqueous suspension comprising cellulosic fibres, (ii) adding to the
suspension after the last point of high shear and subsequent a
centri-screen: (a) a first anionic component which is a
water-soluble anionic polysaccharide; (b) a second anionic
component which is a water-dispersible or branched acrylamide-based
polymer; (c) a third anionic component which is an anionic
siliceous material comprising an anionic silica-based polymer
comprising anionic silica-based particles having a specific surface
area within the range of from 100 to 1700 m2/g; (iii) dewatering
the obtained suspension to form paper; wherein the anionic
polysaccharide is guar gum.
14. The process of claim 13, wherein the first anionic component
has a weight average molecular weight of at least 10,000.
15. The process of claim 13, wherein the anionic silica-based
particles are present in a sol having an S-value in the range of
from 8 to 50%.
16. The process of claim 13, wherein the anionic silica-based
particles have an average particle size in the range of from 1 to
10 nm.
17. The process of claim 13, wherein the anionic silica-based
particles have a specific surface area in the range of from 50 to
1000 m.sup.2/g.
18. The process claim 13, wherein the anionic silica-based
particles have a specific surface area in the range of from 1000 to
1700 m.sup.2/g.
19. The process of claim 13, wherein the second anionic component
is a water-dispersible or branched acrylamide-based polymer
obtained by polymerization of a monomer mixture comprising
polyfunctional crosslinking agents and monomers selected form the
group consisting of anionic monomers selected from the group
consisting of ethylenically unsaturated carboxylic acids and salts
thereof, ethylenically unsaturated sulphonic acids and salts
thereof, and mixtures thereof; and non-ionic monomers selected from
the group consisting of acrylamide, methacrylamide,
N-methyl(meth)acrylamide, N-ethyl(meth)acrylamide,
N-n-propyl(meth)acrylamide, N-isopropyl(meth)acrylamide,
N-n-butyl(meth)acrylamide, N-t-butyl(meth)acrylamide,
N-isobutyl(meth)acrylamide, N-n-butoxymethyl(meth)acrylamide,
N-isobutoxymethyl(meth)acrylamide, N,N-dimethyl(meth)acrylamide,
N,N-dimethyl(meth)acrylamide, dialkylaminoalkyl(meth) acrylamides,
and mixtures thereof.
20. The process of claim 13, wherein the second anionic component
is a water-dispersible or branched acrylamide-based polymer
obtained by polymerization of a monomer mixture comprising
polyfunctional crosslinking agents and monomers selected form the
group consisting of non-ionic monomers selected from the group
consisting of acrylamide, methacrylamide, and mixtures thereof; and
anionic monomers selected from the group consisting of
ethylenically unsaturated carboxylic acids and salts thereof.
Description
FIELD OF THE INVENTION
The present invention relates to a process for the production of
paper and a composition comprising anionic components that is
suitable for use as an additive in papermaking. More specifically,
the invention relates to a process for the production of paper
which comprises adding first, second and third anionic components
to a cellulosic suspension after all points of high shear and
dewatering the obtained suspension to form paper.
BACKGROUND OF THE INVENTION
In the art of papermaking, an aqueous suspension containing
cellulosic fibres, and optional fillers and additives, is fed
through pumps, screens and cleaners, which subject the stock to
high shear forces, into a headbox which ejects the suspension onto
a forming wire. Water is drained from the suspension through the
forming wire so that a wet web of paper is formed on the wire, and
the web is further dewatered and dried in the drying section of the
paper machine. Drainage and retention aids are conventionally
introduced at different points in the flow of suspension in order
to facilitate drainage and increase adsorption of fine particles
such as fine fibres, fillers and additives onto the cellulose
fibres so that they are retained with the fibres on the wire.
Examples of conventionally used drainage and retention aids include
organic polymers, inorganic materials, and combinations
thereof.
WO 98/56715 discloses aqueous polysilicate microgels, their
preparation and use in papermaking and water purification. The
polysilicate microgels can contain additional compounds, e.g.
polymers containing carboxylic acid and sulphonic acid groups, such
as polyacrylic acid.
WO 00/006490 discloses anionic nanocomposites for use as retention
and drainage aids is papermaking prepared by adding an anionic
polyelectrolyte to a sodium silicate solution and then combining
the sodium silicate and polyelectrolyte solution with silicic
acid.
U.S. Pat. No. 6,103,065 discloses a method for improving the
retention and drainage of papermaking furnish comprising the steps
of adding at least one cationic high charge density polymer of
molecular weight 100,000 to 2,000,000 to said furnish after the
last point of high shear; adding at least one polymer having a
molecular weight greater than 2,000,000; and adding a swellable
bentonite clay.
WO 01/34910 discloses a process for making paper or paper board in
which a cellulosic suspension is flocculated by addition of a
substantially water soluble polymer selected from (a) a
polysaccharide or (b) a synthetic polymer of intrinsic viscosity at
least 4 dl/g and then reflocculated by a subsequent addition of a
reflocculating system comprising (i) a siliceous material and (ii)
a substantially water soluble anionic polymer. Preferably, the
substantially water soluble polymer is mixed into the cellulosic
suspension causing flocculation and the flocculated suspension is
then sheared, e.g. by passing it through one or more shear stages.
The water soluble anionic polymeric reflocculating agent is
preferably added late in the process, preferably after the last
point of high shear, e.g. subsequent to the centri-screen. The
process is claimed to provide improvements in retention and
drainage.
WO 02/33171 discloses a process for making paper or paper board in
which a cellulosic suspension is flocculated using a flocculating
system comprising a siliceous material and organic microparticles
which have an unswollen particle diameter of less than 750 nm.
WO 02/101145 discloses an aqueous composition comprising anionic
organic polymeric particles and colloidal anionic silica-based
particles, the anionic organic polymeric particles being obtainable
by polymerising one or more ethylenically unsaturated monomers
together with one or more polyfunctional branching agents and/or
polyfunctional crosslinking agents. The composition is used as a
flocculating agent in dewatering of suspended soils, in the
treatment of water, wastewater and waste sludge, and as drainage
and retention aid in the production of paper.
It would be advantageous to be able to provide a papermaking
process with further improvements in drainage, retention and
formation.
SUMMARY OF THE INVENTION
The present invention is directed to a process for producing paper
which comprises: (i) providing an aqueous suspension comprising
cellulosic fibres, (ii) adding to the suspension after the last
point of high shear: (a) a first anionic component which is a
water-soluble anionic organic polymer; (b) a second anionic
component which is a water-dispersible or branched anionic organic
polymer having an unswollen particle size less than 1000 nm; and
(c) a third anionic component which is an anionic siliceous
material; and (iii) dewatering the obtained suspension to form
paper.
The present invention is further directed to a process for
producing paper which comprises: (i) providing an aqueous
suspension comprising cellulosic fibres, (ii) adding to the
suspension after the last point of high shear: (a) a first anionic
component which is a water-soluble anionic organic polymer; (b) a
second anionic component which is a water-dispersible or branched
anionic organic polymer; and (c) a third anionic component which is
an anionic siliceous material comprising anionic silica-based
polymer which comprises (I) aggregated anionic silica-based
particles; or (II) silica-based particles having a specific surface
area within the range of from 100 to 1700 m2/g (iii) dewatering the
obtained suspension to form paper.
The present invention is further directed to a drainage and
retention aid composition which comprises: (a) a first anionic
component which is a water-soluble anionic organic polymer; (b) a
second anionic component which is a water-dispersible or branched
anionic organic polymer having an unswollen particle size of less
than 1000 nm; and (c) a third anionic component which is an anionic
siliceous material; wherein the first, second and third anionic
components are present in a dry matter content of from 0.01 to 50%
by weight.
The present invention is further directed to a drainage and
retention aid composition which comprises: (a) a first anionic
component which is a water-soluble anionic organic polymer; (b) a
second anionic component which is a water-dispersible or branched
anionic organic polymer; and (c) a third anionic component which is
an anionic siliceous material comprising anionic silica-based
polymer which comprises (I) aggregated anionic silica-based
particles; or (II) silica-based particles having a specific surface
area within the range of from 100 to 1700 m2/g wherein the first,
second and third anionic components are present in a dry matter
content of from 0.01 to 50% by weight.
The present invention further relates to the use of the composition
as a flocculating agent in the production of pulp and paper and for
water purification.
DETAILED DESCRIPTION OF THE INVENTION
According to the present invention it has been found that drainage
and retention can be improved without any significant impairment of
formation, or even with improvements in paper formation, by a
process which comprises adding three different anionic components,
i.e., first, second and third anionic components, to an aqueous
cellulosic suspension after the last point of high shear.
Preferably, after the addition of the first, second and third
anionic components, the obtained cellulosic suspension is fed into
a headbox and ejected onto a wire where it is dewatered to form
paper. Preferably, the cellulosic suspension is pre-treated by
addition of a cationic material before addition of the first,
second and third anionic components.
The present invention provides improvements in drainage and
retention in the production of paper from all types of cellulosic
suspensions, in particular suspensions containing mechanical or
recycled pulp, and stocks having high contents of salts (high
conductivity) and colloidal substances, and in papermaking
processes with a high degree of white water closure, i.e. extensive
white water recycling and limited fresh water supply. Hereby the
present invention makes it possible to increase the speed of the
paper machine and to use lower dosages of polymers to give
corresponding drainage and/or retention effects, thereby leading to
an improved papermaking process and economic benefits.
First Anionic Component
The first anionic component according to the invention is a
water-soluble anionic organic polymer. Examples of suitable
water-soluble anionic organic polymers include anionic
polysaccharides and anionic synthetic organic polymers, preferably
anionic synthetic organic polymers. Examples of suitable
water-soluble anionic synthetic organic polymers include anionic
aromatic condensation polymers and anionic vinyl addition polymers.
Preferably, the water-soluble anionic organic polymer is
substantially linear.
Examples of suitable water-soluble anionic polysaccharides include
anionic starches, guar gums, cellulose derivatives, chitins,
chitosans, glycans, galactans, glucans, xanthan gums, pectins,
mannans, dextrins, preferably starches, guar gums and cellulose
derivatives. Examples of suitable starches include potato, corn,
wheat, tapioca, rice, waxy maize and barley, preferably potato.
Examples of suitable water-soluble anionic aromatic condensation
polymers include anionic benzene-based and naphthalene-based
condensation polymers, preferably naphthalene-sulphonic acid based
and naphthalene-sulphonate based condensation polymers.
Examples of suitable water-soluble anionic synthetic organic
polymers include anionic vinyl addition polymers obtained by
polymerization of a water-soluble ethylenically unsaturated anionic
or potentially anionic monomer or, preferably, a monomer mixture
comprising one or more water-soluble ethylenically unsaturated
anionic or potentially anionic monomers and, optionally, one or
more other water-soluble ethylenically unsaturated monomers. The
term "potentially anionic monomer", as used herein, is meant to
include a monomer bearing a potentially ionisable group which
becomes anionic when included in a polymer on application to the
cellulosic suspension. Examples of suitable anionic and potentially
anionic monomers include ethylenically unsaturated carboxylic acids
and salts thereof, and ethylenically unsaturated sulphonic acids
and salts thereof, e.g. (meth)acrylic acid and salts thereof,
suitably sodium (meth)acrylate, ethylenically unsaturated sulphonic
acids and salts thereof, e.g.
2-acrylamido-2-methylpropanesulphonate, sulphoethyl-(meth)acrylate,
vinylsulphonic acid and salts thereof, styrenesulphonate, and
paravinyl phenol (hydroxy styrene) and salts thereof. Preferably,
the polymerization is carried out in the absence or substantial
absence of crosslinking agent, thereby forming substantially linear
anionic synthetic organic polymers.
The monomer mixture can contain one or more water-soluble
ethylenically unsaturated non-ionic monomers. Examples of suitable
copolymerizable non-ionic monomers include acrylamide and
acrylamide-based monomers, e.g. methacrylamide,
N-alkyl(meth)-acrylamides, e.g. N-methyl(meth)acrylamide,
N-ethyl(meth)acrylamide, N-n-propyl(meth)-acrylamide,
N-isopropyl(meth)acrylamide, N-n-butyl(meth)acrylamide,
N-t-butyl(meth)-acrylamide and N-isobutyl(meth)acrylamide;
N-alkoxyalkyl(meth)acrylamides, e.g.
N-n-butoxymethyl(meth)acrylamide, and
N-isobutoxymethyl(meth)acrylamide; N,N-dialkyl(meth)acrylamides,
e.g. N,N-dimethyl(meth)acrylamide;
dialkylaminoalkyl(meth)acryl-amides; acrylate-based monomers like
dialkylaminoalkyl(meth)acrylates; and vinyl amines. The monomer
mixture can also contain one or more water-soluble ethylenically
unsaturated cationic or potentially cationic monomers, preferably
in minor amounts if present. The term "potentially cationic
monomer", as used herein, is meant to include a monomer bearing a
potentially ionisable group which becomes cationic when included in
a polymer on application to the cellulosic suspension. Examples of
suitable cationic monomers include those represented by the
below-mentioned general structural formula (I), and diallyldialkyl
ammonium halides, e.g. diallyldimethyl ammonium chloride. Examples
of preferred copolymerizable monomers include (meth)acrylamide, and
examples of preferred first anionic components include anionic
acrylamide-based polymer.
The first anionic component according to the invention can have a
weight average molecular weight of at least about 2,000, suitably
at least 10,000. For anionic aromatic condensation polymers, the
weight average molecular weight is usually at least about 2,000,
suitably at least 10,000. For anionic vinyl addition polymers, the
weight average molecular weight is usually at least 500,000,
suitably at least about 1 million, preferably at least about 2
million and more preferably at least about 5 million. The upper
limit is not critical; it can be about 300 million, usually 50
million and suitably 30 million.
The first anionic component according to the invention usually has
a charge density less than about 10 meq/g, suitably less than about
6 meq/g, preferably less than about 4 meq/g, more preferably less
than 2 meq/g. Suitably, the charge density is in the range of from
0.5 to 10.0, preferably from 1.0 to 4.0 meq/g.
Second Anionic Component
The second anionic component according to the invention is a
water-dispersible or branched anionic organic polymer. Preferably,
the second anionic component is a synthetic anionic organic
polymer. Examples of suitable water-dispersible anionic organic
polymers include crosslinked anionic organic polymers and
non-crosslinked water-insoluble anionic organic polymers. Examples
of suitable branched anionic organic polymers include water-soluble
anionic organic polymers.
Examples of suitable water-dispersible and branched anionic organic
polymers include the crosslinked and branched polymers obtained by
polymerization of a monomer mixture comprising one or more
ethylenically unsaturated anionic or potentially anionic monomers
and, optionally, one or more other ethylenically unsaturated
monomers, in the presence of one or more polyfunctional
crosslinking agents. Preferably, the ethylenically unsaturated
monomers are water-soluble. The presence of a polyfunctional
crosslinking agent in the monomer mixture renders possible
preparation of branched polymers, slightly crosslinked polymers and
highly crosslinked polymers that are water-dispersible.
Examples of suitable anionic and potentially anionic monomers
include ethylenically unsaturated carboxylic acids and salts
thereof, ethylenically unsaturated sulphonic acids and salts
thereof, e.g. any one of those mentioned above. Examples of
suitable polyfunctional crosslinking agents include compounds
having at least two ethylenically unsaturated bonds, e.g.
N,N-methylene-bis(meth)acrylamide, polyethyleneglycol
di(meth)acrylate, N-vinyl(meth)acrylamide, divinylbenzene,
triallylammonium salts and N-methylallyl(meth)acrylamide; compounds
having an ethylenically unsaturated bond and a reactive group, e.g.
glycidyl(meth)acrylate, acrolein and methylol(meth)acrylamide; and
compounds having at least two reactive groups, e.g. dialdehydes
like glyoxal, diepoxy compounds and epichlorohydrin.
The monomer mixture can contain one or more water-soluble
ethylenically unsaturated non-ionic monomers. Examples of suitable
copolymerizable non-ionic monomers include acrylamide and the
above-mentioned non-ionic acrylamide-based and acrylate-based
monomers and vinyl amines. The monomer mixture can also contain one
or more water-soluble ethylenically unsaturated cationic or
potentially cationic monomers, preferably in minor amounts if
present. Examples of suitable copolymerizable cationic monomers
include the monomers represented by the above general structural
formula (I) and diallyldialkyl ammonium halides, e.g.
diallyldimethyl ammonium chloride.
Suitable water-dispersible and branched anionic organic polymers
can be prepared using at least 4 molar parts per million of
polyfunctional crosslinking agent based on monomer present in the
monomer mixture, or based on monomeric units present in the
polymer, preferably from about 4 to about 6,000 molar parts per
million, most preferably from 20 to 4,000.
Examples of preferred water-dispersible or branched anionic organic
polymer include water-dispersible and branched anionic
acrylamide-based polymers.
Examples of suitable non-crosslinked water-insoluble anionic
organic polymers include the polymers obtained by polymerization of
a monomer mixture comprising one or more water-insoluble monomers,
one or more ethylenically unsaturated anionic or potentially
anionic monomers and, optionally, one or more other ethylenically
unsaturated monomers. Examples of suitable water-insoluble monomers
include styrene and styrene-based monomers, alkenes, e.g. ethylene,
propylene, butylenes, etc. Examples of suitable anionic and
potentially anionic monomers include ethylenically unsaturated
carboxylic acids and salts thereof, ethylenically unsaturated
sulphonic acids and salts thereof, e.g. any one of those mentioned
above.
Suitable water-dispersible anionic organic polymer have an
unswollen particle size of less than about 1,500 nm in diameter,
suitably less than about 1,000 nm and preferably less than about
950 nm. Examples of suitable water-dispersible and branched anionic
organic polymers include those disclosed in U.S. Pat. No.
5,167,766, which is hereby incorporated herein by reference.
Third Anionic Component
The third anionic component according to the invention is an
anionic siliceous material. Examples of suitable anionic siliceous
materials include anionic inorganic polymers based on silicic acid
and silicates, i.e., anionic silica-based polymers, and clays of
smectite type, preferably anionic polymers based on silicic acid or
silicates.
Suitable anionic silica-based polymers can be prepared by
condensation polymerisation of siliceous compounds, e.g. silicic
acids and silicates, which can be homopolymerised or
co-polymerised. Preferably, the anionic silica-based polymers
comprise anionic silica-based particles that are in the colloidal
range of particle size. Anionic silica-based particles are usually
supplied in the form of aqueous colloidal dispersions, so-called
aqueous sols. The silica-based sols can be modified and contain
other elements, e.g. aluminium, boron, nitrogen, zirconium, gallium
and titanium, which can be present in the aqueous phase and/or in
the silica-based particles. Examples of suitable anionic
silica-based particles include polysilicic acids, polysilicic acid
microgels, polysilicates, polysilicate microgels, colloidal silica,
colloidal aluminium-modified silica, polyaluminosilicates,
polyaluminosilicate microgels, polyborosilicates, etc. Examples of
suitable anionic silica-based particles include those disclosed in
U.S. Pat. Nos. 4,388,150; 4,927,498; 4,954,220; 4,961,825; 4,980,
025; 5,127, 994; 5,176, 891; 5,368,833; 5,447,604; 5,470,435;
5,543,014; 5,571,494; 5,573,674; 5,584,966; 5,603,805; 5,688,482;
and 5,707,493; which are hereby incorporated herein by
reference.
Examples of suitable anionic silica-based particles include those
having an average particle size below about 100 nm, preferably
below about 20 nm and more preferably in the range of from about 1
to about 10 nm. As conventional in the silica chemistry, the
particle size refers to the average size of the primary particles,
which may be aggregated or non-aggregated. Preferably, the anionic
silica-based polymer comprises aggregated anionic silica-based
particles. The specific surface area of the silica-based particles
is suitably at least 50 m.sup.2/g and preferably at least 100
m.sup.2/g. Generally, the specific surface area can be up to about
1700 m.sup.2/g and preferably up to 1000 m.sup.2/g. The specific
surface area is measured by means of titration with NaOH as
described by G. W. Sears in Analytical Chemistry 28(1956): 12,
1981-1983 and in U.S. Pat. No. 5,176,891 after appropriate removal
of or adjustment for any compounds present in the sample that may
disturb the titration like aluminium and boron species. The given
area thus represents the average specific surface area of the
particles.
In a preferred embodiment of the invention, the anionic
silica-based particles have a specific surface area within the
range of from 50 to 1000 m.sup.2/g, more preferably from 100 to 950
m.sup.2/g. Preferably, the silica-based particles are present in a
sol having a S-value in the range of from 8 to 50%, preferably from
10 to 40%, containing silica-based particles with a specific
surface area in the range of from 300 to 1000 m.sup.2/g, suitably
from 500 to 950 m.sup.2/g, and preferably from 750 to 950
m.sup.2/g, which sols can be modified as mentioned above. The
S-value is measured and calculated as described by Iler &
Dalton in J. Phys. Chem. 60(1956), 955-957. The S-value indicates
the degree of aggregation or microgel formation and a lower S-value
is indicative of a higher degree of aggregation.
In yet another preferred embodiment of the invention, the
silica-based particles have a high specific surface area, suitably
above about 1000 m.sup.2/g. The specific surface area can be in the
range of from 1000 to 1700 m.sup.2/g and preferably from 1050 to
1600 m.sup.2/g.
Examples of suitable clays of smectite type include naturally
occurring, synthetic and chemically treated materials, e.g.
montmorillonite, bentonite, hectorite, beidelite, nontronite,
saponite, sauconite, hormonite, attapulgite and sepiolite,
preferably bentonite. Suitable clays include those disclosed in
U.S. Pat. Nos. 4,753,710; 5,071,512; and 5,607,552, which are
hereby incorporated herein by reference.
Additional Components
It may be desirable to further include additional components in the
process of the present invention. Preferably, these components are
added to the cellulosic suspension before it is passed through the
last point of high shear, and these components can be added to the
thick cellulosic suspension or to the thin cellulosic suspension
which can be obtained by mixing the thick cellulosic suspension
with fresh water and/or recirculated white water.
According to a preferred aspect of the invention, the process
comprises adding a cationic material to the cellulosic suspension
before the last point of high shear. Examples of suitable cationic
materials include cationic organic polymers and cationic inorganic
materials.
Examples of suitable cationic organic polymers include cationic
polysaccharides, cationic synthetic polymers and cationic organic
flocculants. Examples of suitable cationic inorganic materials
include cationic inorganic coagulants.
Examples of suitable cationic polysaccharides include cationic
starches, guar gums, cellulose derivatives, chitins, chitosans,
glycans, galactans, glucans, xanthan gums, pectins, mannans,
dextrins, preferably starches, guar gums and cellulose derivatives.
Examples of suitable starches include potato, corn, wheat, tapioca,
rice, waxy maize and barley, preferably potato.
Examples of suitable cationic synthetic polymers include
water-soluble high molecular weight cationic synthetic organic
polymers, e.g. cationic acrylamide-based polymers;
poly(diallyl-dialkyl ammonium halides), e.g. poly(diallyldimethyl
ammonium chloride); polyethylene imines; polyamidoamines;
polyamines; and vinylamine-based polymers. Examples of suitable
water-soluble high molecular weight cationic synthetic organic
polymers include polymers prepared by polymerization of a
water-soluble ethylenically unsaturated cationic or potentially
cationic monomer or, preferably, a monomer mixture comprising one
or more water-soluble ethylenically unsaturated cationic or
potentially cationic monomers and optionally one or more other
water-soluble ethylenically unsaturated monomers.
Examples of suitable water-soluble ethylenically unsaturated
cationic monomers include diallyldialkyl ammonium halides, e.g.
diallyldimethyl ammonium chloride and cationic monomers represented
by the general structural formula (I):
##STR00001## wherein R.sub.1 is H or CH.sub.3; R.sub.2 and R.sub.3
are each H or, preferably, a hydrocarbon group, suitably alkyl,
having from 1 to 3 carbon atoms, preferably 1 to 2 carbon atoms; A
is O or NH; B is an alkyl or alkylene group having from 2 to 8
carbon atoms, suitably from 2 to 4 carbon atoms, or a hydroxy
propylene group; R.sub.4 is H or, preferably, a hydrocarbon group,
suitably alkyl, having from 1 to 4 carbon atoms, preferably 1 to 2
carbon atoms, or a substituent containing an aromatic group,
suitably a phenyl or substituted phenyl group, which can be
attached to the nitrogen by means of an alkylene group usually
having from 1 to 3 carbon atoms, suitably 1 to 2 carbon atoms,
suitable R.sub.4 including a benzyl group
(--CH.sub.2--C.sub.6H.sub.5); and X is an anionic counterion,
usually a halide like chloride.
Examples of suitable monomers represented by the general structural
formula (I) include quaternary monomers obtained by treating
dialkylaminoalkyl(meth)acrylates, e.g.
dimethylaminoethyl(meth)acrylate, diethylaminoethyl(meth)acrylate
and dimethylaminohydroxypropyl(meth)acrylate, and
dialkylaminoalkyl(meth)acrylamides, e.g.
dimethylaminoethyl(meth)-acrylamide,
diethylaminoethyl(meth)acrylamide,
dimethylaminopropyl(meth)acrylamide, and
diethylaminopropyl(meth)acrylamide, with methyl chloride or benzyl
chloride. Preferred cationic monomers of the general formula (I)
include dimethylaminoethyl acrylate methyl chloride quaternary
salt, dimethylaminoethyl methacrylate methyl chloride quaternary
salt, dimethylaminoethyl acrylate benzyl chloride quaternary salt
and dimethylaminoethyl methacrylate benzyl chloride quaternary
salt.
The monomer mixture can contain one or more water-soluble
ethylenically unsaturated non-ionic monomers. Examples of suitable
non-ionic monomers include acrylamide and the above-mentioned
non-ionic acrylamide-based and acrylate-based monomers and vinyl
amines. The monomer mixture can also contain one or more
water-soluble ethylenically unsaturated anionic or potentially
anionic monomers, preferably in minor amounts if present. Examples
of suitable copolymerizable anionic and potentially anionic
monomers include ethylenically unsaturated carboxylic acids and
salts thereof, and ethylenically unsaturated sulphonic acids and
salts thereof, e.g. any one of those mentioned above. Examples of
preferred copolymerizable monomers include acrylamide and
methacrylamide, i.e. (meth)acrylamide, and examples of preferred
high molecular weight cationic synthetic organic polymers include
cationic acrylamide-based polymer.
The high molecular weight cationic synthetic organic polymers can
have a weight average molecular weight of at least 500,000,
suitably at least about 1 million and preferably above about 2
million. The upper limit is not critical; it can be about 30
million, usually 20 million.
Examples of suitable cationic organic coagulants include cationic
polyamines, polyamideamines, polyethylene imines, dicyandiamide
condensation polymers and low molecular weight highly cationic
vinyl addition polymers. Examples of suitable cationic inorganic
coagulants include aluminium compounds like alum and polyaluminium
compounds, e.g. polyaluminium chlorides.
Addition of Components
According to the present invention, the first, second and third
anionic components are added to the aqueous cellulosic suspension
after it has passed through all stages of high mechanical shear and
prior to drainage. Examples of high mechanical shear stages include
pumping and cleaning stages. For instance, such shearing stages are
included when the cellulosic suspension is passed through fan
pumps, pressure screens and centri-screens. Suitably, the last
point of high shear occurs at a centri-screen and, consequently,
the first, second and third anionic components are suitably added
to the cellulosic suspension subsequent to the centri-screen.
Preferably, after addition of the first, second and third anionic
components the cellulosic suspension is fed into the headbox of the
paper machine which ejects the suspension onto the forming wire for
drainage.
The first, second and third anionic components can be separately or
simultaneously added to the cellulosic suspension. When separately
adding the components, they can be added in any order. Suitably,
the first anionic component is added prior to adding the second and
third anionic components, the second component can be added prior
to, simultaneously with or after the third component.
Alternatively, the first anionic component is suitably added to the
cellulosic suspension simultaneously with the second anionic
component and then the third anionic component is added.
When simultaneously adding the components, the first, second and
third anionic components can be added separately and/or in the form
of a mixture. Examples of suitable simultaneous additions include
adding the three components separately, and adding one of the
components separately and two of the components in the form of a
mixture. The present invention further relates to a composition
comprising the above-mentioned first, second and third components
and the use thereof. Suitably, the composition is used as a
flocculating agent in the production of pulp and paper and for
water purification. Preferably, the composition is used as a
drainage and retention aid in papermaking, optionally in
combination with a cationic material, e.g. any one of the cationic
materials disclosed herein. Preferably, the composition is aqueous
and the first, second and third anionic components can be present
in a dry matter content of from 0.01 to 50% by weight, suitably
from 0.1 to 30% by weight. The first (1.sup.st), second (2.sup.nd)
and third (3.sup.rd) anionic components can be present in the
composition in a weight ratio 1.sup.st:2.sup.nd:3.sup.rd of
0.05-10:0.05-10:1, preferably 0.1-2:0.1-2:1. The composition
according to the invention can be easily prepared by mixing the
first, second and third components, preferably under stirring.
The first, second and third anionic components according to the
invention can be added to the cellulosic suspension to be dewatered
in amounts which can vary within wide limits.
Generally, the first, second and third anionic components are added
in amounts that give better drainage and retention than is obtained
when not adding the polymers. The first anionic component is
usually added in an amount of at least about 0.001% by weight,
often at least about 0.005% by weight, calculated as dry polymer on
dry cellulosic suspension, and the upper limit is usually about 2.0
and suitably about 1.5% by weight. Likewise, the second anionic
component is usually added in an amount of at least about 0.001% by
weight, often at least about 0.005% by weight, calculated as dry
polymer on dry cellulosic suspension, and the upper limit is
usually about 2.0 and suitably about 1.5% by weight. Similarly, the
third anionic component is usually added in an amount of at least
about 0.001% by weight, often at least about 0.005% by weight,
calculated as dry additive (usually dry SiO.sub.2 or dry clay) on
dry cellulosic suspension, and the upper limit is usually about 2.0
and suitably about 1.5% by weight. When using the composition
according to the invention, it is usually added in an amount of at
least about 0.003% by weight, often at least about 0.005% by
weight, calculated as dry matter on dry cellulosic suspension, and
the upper limit is usually about 5.0 and suitably about 3.0% by
weight.
When using a cationic material in the process, such a material can
be added in an amount of at least about 0.001% by weight,
calculated as dry material on dry cellulosic suspension. Suitably,
the amount is in the range of from about 0.05 up to about 3.0%,
preferably in the range from about 0.1 up to about 2.0%.
The process of this invention is applicable to all papermaking
processes and cellulosic suspensions, and it is particularly useful
in the manufacture of paper from a stock that has a high
conductivity. In such cases, the conductivity of the stock that is
dewatered on the wire is usually at least about 1.0 mS/cm,
preferably at least 3.0 mS/cm, and more preferably at least 5.0
mS/cm. Conductivity can be measured by standard equipment such as,
for example, a WTW LF 539 instrument supplied by Christian
Berner.
The present invention further encompasses papermaking processes
where white water is extensively recycled, or recirculated, i.e.
with a high degree of white water closure, for example where from 0
to 30 tons of fresh water are used per ton of dry paper produced,
usually less than 20, preferably less than 15, more preferably less
than 10 and notably less than 5 tons of fresh water per ton of
paper. Fresh water can be introduced in the process at any stage;
for example, fresh water can be mixed with cellulosic fibres in
order to form a cellulosic suspension, and fresh water can be mixed
with a thick cellulosic suspension to dilute it so as to form a
thin cellulosic suspension to which the first, second and third
anionic components are subsequently added.
The process according to the invention is used for the production
of paper. The term "paper", as used herein, of course include not
only paper and the production thereof, but also other web-like
products, such as for example board and paperboard, and the
production thereof. The process can be used in the production of
paper from different types of suspensions of cellulosic fibres, and
the suspensions should preferably contain at least 25% and more
preferably at least 50% by weight of such fibres, based on dry
substance. The suspensions can be based on fibres from chemical
pulp, such as sulphate and sulphite pulp, thermo-mechanical pulp,
chemo-thermomechanical pulp, organosolv pulp, refiner pulp or
groundwood pulp from both hardwood and softwood, or fibres derived
from one year plants like elephant grass, bagasse, flax, straw,
etc., and can also be used for suspensions based on recycled
fibres. The invention is preferably applied to processes for making
paper from wood-containing suspensions.
The suspension also contain mineral fillers of conventional types,
such as, for example, kaolin, clay, titanium dioxide, gypsum, talc
and both natural and synthetic calcium carbonates, such as, for
example, chalk, ground marble, ground calcium carbonate, and
precipitated calcium carbonate. The stock can of course also
contain papermaking additives of conventional types, such as
wet-strength agents, sizing agents, such as those based on rosin,
ketene dimers, ketene multimers, alkenyl succinic anhydrides,
etc.
Preferably the invention is applied on paper machines producing
wood-containing paper and paper based on recycled fibres, such as
SC, LWC and different types of book and newsprint papers, and on
machines producing wood-free printing and writing papers, the term
wood-free meaning less than about 15% of wood-containing fibres.
Examples of preferred applications of the invention include the
production of paper and layer of multilayered paper from cellulosic
suspensions containing at least 50% by weight of mechanical and/or
recycled fibres. Preferably the invention is applied on paper
machines running at a speed of from 300 to 3000 m/min and more
preferably from 500 to 2500 m/min.
The invention is further illustrated in the following example
which, however, is not intended to limit the same. Parts and %
relate to parts by weight and % by weight, respectively, unless
otherwise stated.
EXAMPLE 1
The following components were used in the examples to illustrate
the present invention: A1: Water-soluble anionic acrylamide-based
polymer prepared by polymerisation of acrylamide (80 mole %) and
acrylic acid (20 mole %), the polymer having a weight average
molecular weight of about 12 million and anionic charge density of
about 2.6 meq/g. A2: Water-dispersible crosslinked anionic
acrylamide-based polymer prepared by polymerisation of acrylamide
(30 mole %), acrylic acid (70 mole %) in he presence of
N,N-methylene-bis(meth)acrylamide as a crosslinking agent (350
ppm), the polymer having an anionic charge density of about 8.5
meq/g. A3: Anionic inorganic condensation polymer of silicic acid
in the form of colloidal aluminium-modified silica sol having an
S-value of about 21 and containing silica-based particles with a
specific surface area of about 800 m.sup.2/g. A123: A mixture of
the above A1, A2 and A3 in a dry weight ratio A1:A2:A3 of
0.2:0.2:1. C1: Cationic polyaluminium chloride with a cationic
charge density of about 8.0 meqv/g. C2: Cationic acrylamide-based
polymer prepared by polymerisation of acrylamide (90 mole %) and
acryloxyethyltrimethyl ammonium chloride (10 mole %), the polymer
having a weight average molecular weight of about 6 million and
cationic charge density of about 1.2 meq/g. C3: Cationic
acrylamide-based polymer prepared by polymerisation of acrylamide
(60 mole %) and acryloxyethyltrimethyl ammonium chloride (40 mole
%), the polymer having a weight average molecular weight of about 3
million and cationic charge of about 3.3 meq/g. C4: Cationic starch
prepared by treating native starch with 2,3-hydroxypropyl trimethyl
ammonium chloride to achieve D.S. 0.11, the polymer having a
cationic charge density of about 0.6 meq/g.
EXAMPLE 2
Drainage performance was evaluated by means of a Dynamic Drainage
Analyser (DDA), available from Akribi, Sweden, which measures the
time for draining a set volume of cellulosic suspension through a
wire when removing a plug and applying vacuum to that side of the
wire opposite to the side on which the cellulosic suspension is
present.
Retention performance was evaluated by means of a nephelometer,
available from Novasina, Switzerland, by measuring the turbidity of
the filtrate, the white water, obtained by draining the cellulosic
suspension. The turbidity was measured in NTU (Nephelometric
Turbidity Units).
The cellulosic suspension used in the test was based on 75% TMP and
25% DIP fibre material and bleach water from a newsprint mill.
Consistency was 0.60%, pH was 7.4 and conductivity of the
cellulosic suspension was 1.5 mS/cm.
In order to simulate additions before and after the last points of
high shear, the cellulosic suspension was stirred in a baffled jar
at different stirrer speeds. The stirring and creation of high
shear conditions were made according to the following: (i) stirring
at 1000 rpm for 25 seconds; (ii) stirring at 2000 rpm for 10
seconds; (iii) stirring at 1000 rpm for 15 seconds; and (iv)
dewatering the stock.
Additions to the cellulosic suspension were made as follows
(addition levels in kg/t): Additions, if any, were made 45, 25, 15,
10 and 5 seconds prior to dewatering, corresponding to the
additions designated Add. 45, Add. 25, Add. 15, Add. 10 and Add. 5,
respectively, of Table 1. The additions designated Add. 15, Add. 10
and Add. 5 were accordingly made after the last point of high
shear.
Table 1 shows the drainage (dewatering) and retention effect
observed. In Table 1, Drain. Time means drainage (dewatering) time
and Turb. means turbidity. The addition levels are given as dry
additive (calculated as dry polymer, dry Al.sub.2O.sub.3 and dry
SiO.sub.2) on dry cellulosic suspension.
Test No. 1 shows the result without any additives. Test Nos. 2 to 4
illustrate processes employing additives used for comparison and
Test Nos. 5 to 15 illustrate processes according to the
invention.
TABLE-US-00001 TABLE 1 Addition Levels at Add. 45/Add. 25/ Drain.
Test Add. Add. Add. Add. Add. Add. 15/Add. 10/ Time Turb. No. 45 25
15 10 5 Add. 5 [kg/t] [s] [NTU] 1 -- -- -- -- -- --/--/--/--/--
65.1 202 2 C1 A2 A1 A3 -- 2/0.1/0.1/0.5/-- 51.3 128 3 C1 A3 A1 --
A2 2/0.5/0.1/--/0.1 41.0 110 4 C1 A1 -- A3 A2 2/0.1/--/0.5/0.1 43.3
150 5 C1 -- A1 A3 A2 2/--/0.1/0.5/0.1 39.7 126 6 -- C2 A1 A3 A2
--/1.5/0.1/0.5/0.1 36.3 95 7 -- C2 A1 A3 A2 --/2/0.1/0.5/0.1 21.8
65 8 -- C2 A1 A2 A3 --/2/0.1/0.1/0.5 18.1 69 9 -- C2 A2 A1 A3
--/2/0.1/0.5/0.1 18.3 69 10 -- C2 A2 A3 A1 --/2/0.1/0.5/0.1 33.5 76
11 -- C2 A3 A1 A2 --/2/0.5/0.1/0.1 19.9 67 12 -- C2 A3 A2 A1
--/2/0.5/0.1/0.1 25.7 67 13 -- C2 A1 + -- -- --/2/0.1 + 0.5 + 20.5
65 A2 + A3 0.1/--/-- 14 -- C2 -- A1 + -- --/2/--/0.1 + 18.5 70 A2 +
A3 0.5 + 0.1/-- 15 -- C2 -- -- A1 + --/2/--/--/0.1 + 17.3 67 A2 +
A3 0.5 + 0.1
As is evident from Table 1, the processes according to the
invention provided improved drainage and retention performance in
view of the comparative processes.
EXAMPLE 3
Drainage performance was evaluated using the procedure according to
Example 2. The cellulosic suspension used in the tests was based on
75% TMP and 25% DIP fibre material and bleach water from a
newsprint mill. Consistency was 0.94%, pH was 7.1 and conductivity
of the cellulosic suspension was 1.4 mS/cm.
Table 2 shows the drainage (dewatering) effect observed. The
addition levels are given as dry additive (calculated as dry
polymer and dry SiO.sub.2) on dry cellulosic suspension.
Test No. 1 shows the result without any additives. Test Nos. 2 to 7
illustrate processes employing additives used for comparison and
Test Nos. 8 to 10 illustrate processes according to the invention.
In Test No. 9, the components A1, A2 and A3 were separately added
10 seconds prior to dewatering. In Test No. 10, the components A2
and A3 were separately added 5 seconds prior to dewatering.
TABLE-US-00002 TABLE 2 Addition Levels at Add. 45/Add. 25/ Drain.
Test Add. Add. Add. Add. Add. Add. 15/Add. 10/ Time No. 45 25 15 10
5 Add. 5 [kg/t] [s] 1 -- -- -- -- -- --/--/--/--/-- 71.8 2 -- C2 --
-- -- --/1/--/--/ 33.2 3 C3 C2 -- -- -- 0.5/1/--/--/-- 26.1 4 C3 C2
-- -- A3 1/1/--/--/0.1 14.3 5 C3 C2 A1 A2 -- 1/1/0.1/0.1/-- 14.2 6
C3 C2 A1 -- A3 1/1/0.1/--/0.1 12.5 7 C3 C2 -- A2 A3 1/1/--/0.1/0.1
10.2 8 C3 C2 A1 A2 A3 1/1/0.1/0.1/0.1 10.0 9 C3 C2 -- A1 + --
1/1/--/0.1 + 9.5 A2 + A3 0.1 + 0.1/-- 10 C3 C2 A1 -- A2 + A3
1/1/0.1/--/0.2 + 9.3 0.1
As is evident from Table 2 the processes according to the invention
provided improved drainage and retention performance in view of the
comparative processes.
EXAMPLE 4
Retention performance was evaluated using the procedure of Example
2. The cellulosic suspension used in the tests was based on 75% TMP
and 25% DIP fibre material and bleach water from a newsprint mill.
Consistency was 0.61%, pH was 7.7 and conductivity of the
cellulosic suspension was 1.6 mS/cm.
Table 3 shows the retention effect observed. The addition levels
are given as dry additive (calculated as dry polymer and dry
SiO.sub.2) on dry cellulosic suspension.
Test No. 1 shows the result without any additives. Test Nos. 2 to
11 illustrate processes employing additives used for comparison and
Test Nos. 12 to 15 illustrate processes according to the invention.
In Test No. 13, the components A1, A2 and A3 were separately added
10 seconds prior to dewatering. In Test Nos. 14 and 15, the
components A1, A2 and A3 were pre-mixed to form the component A123
which was added 10 and 5 seconds, respectively, prior to
dewatering.
TABLE-US-00003 TABLE 3 Addition Levels at Add. 45/Add. 25/ Test
Add. Add. Add. Add. Add. Add. 15/Add. 10/ Turb. No. 45 25 15 10 5
Add. 5 [kg/t] [NTU] 1 -- -- -- -- -- --/--/--/--/-- 143 2 C3 C4 --
-- A3 0.5/5/--/--/1 80 3 C3 C4 A1 -- -- 0.5/5/0.2/--/-- 84 4 C3 C4
-- A2 -- 0.5/5/--/0.2/-- 76 5 C3 C4 A1 -- A3 0.5/5/0.2/--/1 76 6 C3
C4 -- A2 A3 0.5/5/--/0.2/1 68 7 C3 C4 A1 A2 -- 0.5/5/0.2/0.2/-- 69
8 C3 C4 A1 -- -- 0.5/5/0.4/--/-- 79 9 C3 C4 -- A2 --
0.5/5/--/0.4/-- 71 10 C3 C4 A1 -- A3 0.5/5/0.1/--/1 77 11 C3 C4 --
A2 A3 0.5/5/--/0.4/1 70 12 C3 C4 A1 A2 A3 0.5/5/0.2/0.2/1 64 13 C3
C4 -- A1 + -- 0.5/5/--/0.2 + 64 A2 + A3 0.2 + 1/-- 14 C3 C4 -- A123
-- 0.5/5/--/0.2 + 64 0.2 + 1/-- 15 C3 C4 -- -- A123 0.5/5/--/--/ 65
0.2 + 0.2 + 1
As is evident from Table 3, the processes according to the
invention provided improved drainage and retention performance in
view of the comparative processes.
* * * * *
References